Modern wireless networks use Code-Division Multiple Access (CDMA) technology to share frequency across multiple users and applications. To provide continual coverage and thereby maintain Quality of Service (QoS), CDMA supports a “soft handoff.” In soft handoff, a mobile user communicates with a mobile switching center via two or more base transceiver station (BTS) sites and user data is broadcast and received by a number of the sites. This mode of communication makes the mobile-to-cell link resilient to obstructions in the beam path that can cause the active call to terminate abruptly. For example, for the mobile to drop a call, the paths to all of the cells would have to be obstructed.
During soft handoff, radio frames from each link of the handoff are typically compared based on a cyclic redundancy code (CRC) and a selected data frame is passed on to the network while the remaining redundant frames are discarded.
In the CRC method, a CRC character based upon the number if bits in the frame is calculated and added to the data block before the block is transmitted. The receiving end makes a similar calculation and compares its result with the CRC character. If the comparison indicates a difference, a mistake in transmission is indicated. In a wireless link, a CRC value is sent from the BTS along with the frame for soft handoff selection.